Design Study: 3D Printed Tenkara Line Winding System

Article by Guenther Shepherd

I’m an avid tenkara angler and aspiring industrial designer. As part of my independent study in industrial design, I set out to make tenkara gear. In just under 15 months I undertook the process of turning an idea into a product. That process: inspiration, prototyping, and refining is the story I’m going to tell here.

I’ve been tenkara fishing for years and I’ve cycled through a lot of gear in that time. Like most anglers, my kit started small. I hit the creek barefoot with the basics stuffed in my pockets. As the seasons passed my skills grew, and so did the size of my tackle bag. Days on the water grew long and heavy with gear. In recent years my focus has been on the fundamentals, and my kit has been paired down to match. These days I fish with less gear, but I don’t feel limited. I think many tenkara anglers can relate to this journey, after all, simplicity is a recurring motif in tenkara. However, this emphasis on the essentials makes tenkara difficult to design gear for. With tenkara anglers walking out the door with hardly more than a line spool in their pocket, only the best gear makes the cut.

So, let’s talk about line spools. Line spools are one of the few pieces of kit you can’t leave the house without; they are the atomic tool of line management. Available in a variety of shapes and sizes, each is optimized for something slightly different. At first glance, improving their design might seem like trying to reinvent the wheel. But here’s my question: are line spools actually good for line management?

Let me back up a little. Some years ago, I tinkered with attaching reels to tenkara rods. Although this experiment was a dead-end for tenkara rod innovation, it did expose me to something interesting. For the first time, I was managing tenkara line with a reel, and I loved it. The speed, reliability, and convenience were a considerable step up from hand winding spools. This experience left me wondering if there was any way to bring the advantages of reels to tenkara line management.

So that’s exactly what I set out to do. My idea is a hand-held winding reel. It winds onto line spools, that are swappable, and the whole thing is slim enough to fit in a pocket.

The first order of business was designing the spools. My requirements were that it work on every type of line, lockdown both ends of the line, and feature some mechanism for clipping into the winding tool. I drew my requirements from existing spool designs. The ever-popular line-cards are wonderfully thin and work on every line, but they’ve jabbed me countless times with unsecured hook tips. The bitter end of a level line isn’t much better secured and always seems to wiggle free in my pack. The lesser-known Oni Shuriken is possibly the best designed line spool, compact, durable, and cleverly securing both the hook tip and level line end. Sadly, it only works with level lines, “on-brand” for Oni.

Building out the spool functionality proved difficult, and progress was slow. I was able to make prototypes that met my requirements but only barely. It was at this time that I developed the magnetic clutch that allows the spools to stack, their most distinctive feature. I had elected to make them attach to the winding tool using magnets and it followed naturally that the spools could magnetically clip to each other too. While the spools were functional, I couldn’t say they were better than anything already on the market. Improvements from each iteration of this spool design were diminishing and I was starting to question my approach. With stalling progress, I switched over to working on the winding tool.

Requirements for the winder were much simpler. It just needs to wind line and fit in a pocket. At this stage I chose to build the winding mechanism around a planetary gearbox. Planetary gearboxes are compact, but the downside is the complexity of assembly. I, however, had a little trick I planned to use to beat this downside. Something I will discuss later is how using a planetary gearbox would come to haunt me. The rest of the winding assembly was developed just enough to get a working prototype up and running.

At this point I should mention that everything I was designing was also being optimized for an emerging manufacturing technique: 3D printing. While 3D printing isn’t new, the plummeting cost of machine time has made it viable to manufacture end-use products on a 3D printer. This approach makes iteration fast and skips the up-front costs of injection molding. The drawback of this approach is having to design around the limits of 3D printers. I won’t go into the details here, but this is a non-trivial task, and it was slowing down my development of both the line winder and the spools.

With a fully functional winder and spools I hit the water for some testing. Results were abysmal, the system was tedious, unreliable, and bulky. Having a good idea is one thing, making it work is another. I had reached my limitations as a designer, and as hard as it was to admit, I lacked the skills to push it further. Reluctantly, I shelved the project here.

I worked on other projects for about a year and returned to this project late on the following winter. This time would be different: I was fluent in 3D modeling, I knew the quarks of 3D printers, and I had a deeper grasp of the design process. I sat down with a blank canvas and got to work. The first order of business was fixing the winder. I did a grip study, exploring what shapes worked in the hand. From there, I steadily built the functionality of the winder into that shell, skipping the gearbox entirely and just adding a 1:1 winding mechanism for testing. I ditched the old approach of using a knob to turn the winding mechanism in favor of a finger divot. Something much like the ones in old rotary phone dials. Without any protrusions, the design was finally pocket sized.

The gearbox proved to be a challenge. The key was balancing the torque the user could apply, with the drag of the line. When geared too fast, the winder would slam to a stop if the line got the slightest bit snagged. On the other hand, too low of a ratio would make the winder feel “slow,” with hardly any backpressure on the user.

I experimentally determined the ideal ratio between the spool and winder to be about 2:1. Remember how I said using a planetary gearbox would come back to haunt me? Here’s the problem, a planetary gearbox cannot produce a ratio of 2:1 when configured this way. The size of the gears approach infinity as the ratio approaches 2:1. Eventually, I was able to 3D print gear teeth fine enough to get a ratio around 5:2. This is the reason that the gearbox fills the entire winding housing in the final design.

Another note on the gear box is the assembly. Due to quarks of 3D printing, some mechanisms can be 3D printed in their fully-assembled state. Planetary gear boxes are one of those mechanisms, and this was the assembly trick I had mentioned before. This allows the entire gearbox to be 3D printed in its fully assembled state inside of the winder.

The spools were my next task. I was previously held back by the complexity of designing parts for 3D printing. With a fresh approach and an improved skillset, I was able to march the spools past their prior stagnation. Taking advantage of a 3D printing technique called “bridging” I was able to get the spool assembly down from three parts to just two. I was also able to fully flush out the mechanism that secures the bitter end of the tenkara line, finally allowing it to secure even the most slippery level lines. With the old problems solved, I was free to develop the spools distinctive magnetic clutch.

Adding a magnet to the center of a tenkara spool creates an interesting problem. When pulling line off a spool, an angler will usually pitch their thumb and index finger though the hole in the center of the spool. This creates an axel for the spool to spin around as line is pulled out. However, adding a magnet to the center blocks this axel and the slippery surface of the magnet causes the spool to spin-out of the pinch grip. I experimented with dish-shaped magnets and annular magnets, but the solution was shockingly simple. By recessing the magnet into the spool, the slippery surface works like a flat bearing, allowing the spool to self-center in a pinch grip. This was the final touch needed to round off the distinctive design of the line spools.

As the iterations passed, improvements started to stall. I had implemented everything I had dreamed up and I had nothing more to add. As winter passed into spring, I took my little invention fishing.

The final design was by far the most nuanced device I had designed to date. Not long ago this project had defeated me, so its completion gave me a deep sense of progress. I created something I’m proud of, and something that I wanted to share. I’ve been selling my tenkara line system at TeaAndTrout.com for 5 months now and the feedback has been excellent. My hope is that I’ve made something worthy of the tenkara angler’s tackle bag.

Feeling inspired by this story? Want to try your hand at making something too? Here’s my advice on getting started in 3D printing gadgets. Firstly, you’ll need a 3D printer. A printer from any of the big brands will do but expect to spend at least $300. These days you can get a 3D printer out of the box and running in no time, but you’ll need to learn the fundamentals before you’re ready to design your own models. Get familiar with your machine by downloading some models and seeing how they print. There’s plenty of great gadgets you can download from websites like Printables, or Makerworld. Pay close attention to what works and what doesn’t, not all designs are equal.

Once you’re familiar with the printer, it’s time to start designing. You’ll need to get set up in some 3D modeling software, preferably CAD. It can be intimidating to get started with CAD, but I’d advise against settling for less than engineering grade software. There’s no shortage of tutorials to get you set up with the basics. Keep your first couple projects small and keep building your skills. The process is the point, don’t rush it. Share what you make with the world: connect and contribute. The rest is up to you.

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Guenther Shepherd is an engineer and designer with a passion for the outdoors. As a denizen of the Pacific Northwest, he can often be found hiking and fishing high in the Cascades. Learn more on his personal website GuentherShepherd.design.

This article originally appeared in the 2026 print issue of Tenkara Angler magazine.

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